A method of fabricating sheet metal parts comprising
It has been known for some time that steel properties can be enhanced by heat treatment. Heat treatment generally improves the mechanical properties of a part by making it harder and stronger. Heat treatment can comprise of heating, quenching and subsequent annealing. Quenching comprises the rapid cooling of steel by emersion in liquids or gases or by contact with metal in order to harden the part. Annealing, on the other hand, comprises a heating and cooling operation employing usually slow cooling. In annealing the treatment of the operation of the rate of cooling depends upon the material being heat treated and the purpose of the treatment.
Metal parts may be made by a variety of processes including metal stamping. Metal stamping is the forming of metal by using a die and a punch that resembles the shape of the part. The metal stamping may be a hot or cold process. During the metal stamping process the part may either be shaped or formed which implies that the metal is bent or it may be punched which implies that the metal is cut as well as being formed.
Accordingly, stamping may be defined as the hot or cold forming of sheet metal by using a die and punch that resembles the shape of the part. The sheet metal is generally the metal of choice in stamping and comprises of metal of any thickness that is the form of a sheet which has one dimension much smaller compared to the other two dimensions. Usually the sheet metal can comprise of a thickness of 0.5 to 3 mm (0.020 to 0.120 inches).
During the stamping process the sheet metal is formed by using a die and a punch. A die is a tool that forms the part and generally comprises the male shape, while the punch is a tool that also forms the part and generally comprises the female shape.
The concept of forming the part from the soft material first and then once the material is formed heat treating it to improve the strength is very attractive and has been used for many years for low volume production. However, parts that have been formed and then heat treated are severely distorted and show little consistency in shape. Accordingly, the process has not been used in mass production of stampings.
One example of the prior art methods and apparatus can be illustrated by referring to U.S. Pat. No. 5,163,603 which relates to a process of manufacturing hollow triangular upper control arms by stamping a metal body forming an integral portion of the control arm and having a pair of opposing edges, bending the body along two substantially parallel lines and bringing the ends into mutual contact thereby forming a hollow modular section having substantially triangular cross-sectional configuration, welding to permanently join the edges, and piercing a plurality of apertures along the modular section for improving the harmonic resonancy.
Moreover, U.S. Pat. No. 3,068,564 relates to a method of producing laminated metal strips and more particularly to laminating under heat and pressure only.
Yet another method of laminating metal foil and particularly two double sheets of foil which are rolled together in close face-to-face contact and coiled as a single sheet is disclosed in U.S. Pat. No. 2,529,884.
Moreover, U.S. Pat. No. 2,244,847 relates to a method of making structural elements of sheet metal, while U.S. Pat. No. 2,159,043 relates to the making, handling and working of metal members and more particularly to pressure control expedience to be employed during the conditioning, working and handling of such members.
It is an object of this invention to produce sheet metal parts with minimal distortion. More particularly, it is an object of this invention to provide an improved method of fabricating sheet metal parts having little distortion after heat treatment.
The broadest aspect of the invention relates to a method of producing a sheet metal part comprising the steps of: placing a pair of overlying metal sheets in a press and simultaneously forming said metal sheets to a desired shape; heat treating said formed metal sheets so as to increase the mechanical properties of said formed metal sheets and distort said formed metal sheets from said desired shape; clamping said formed heat treated metal sheets together so as to bend said distorted metal sheets back to said desired shape; welding said clamped heat treated metal sheets together to produce said part with said metal sheets with said desired shape.
It is another aspect of this invention to provide a method of fabricating a sheet metal part comprising the steps of: stamping at least a pair of overlying metal sheets simultaneously to form at least a pair of stampings having a desired shape; heat treating said stampings so as to increase the mechanical properties of said stampings, said stampings exhibiting distortion from said desired shape by said heat treatment; clamping said stampings together to bend said distorted heat treated stampings to said desired shape and correct distortion of said stampings; welding said clamped stampings together to control said distortion and to produce said part with said desired shape and increased mechanical properties.
In metal stamping it is generally important to have material that is easily formable. Formability of the part means ease of changing shape. In other words, it is better to have material as soft as possible since it may be easier to stamp.